Integrable tunable filter circuit comprising a set of BAW resonators

ABSTRACT

A tunable filter circuit having inputs IN 1 -IN 2  and outputs OUT 1 -OUT 2 , comprising at least a primary four-pole circuit including in cascade: a first varactor having a first electrode connected to IN 1  and a second electrode; a first inductive resistor connected between the second electrode of the varactor and input IN 2 , a secondary four-pole circuit comprising four BAW resonators. First and second of these resonators have a first electrode connected to a first input of the secondary four-pole circuit and a second electrode connected to first and second outputs of the secondary four-pole circuit, respectively. Similarly, third and fourth of these resonators have a first electrode connected to a second input of the secondary four-pole circuit and a second electrode connected to the second and first outputs of the secondary four-pole circuit, respectively. The circuit further comprises a second inductive resistor connected in parallel to the first and second outputs of the secondary four-pole circuit and a second varactor having a first electrode connected to the first output of the secondary four-pole circuit and a second electrode for connecting a second primary four-pole circuit having the same structure. This allows realization of a particularly effective tunable filter circuit with only four inductive resistors.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of and claims priority under 35U.S.C. §120 from U.S. patent application Ser. No. 11/377,925, filed Mar.16, 2006, now U.S. Pat. No. 7,492,242, issued Feb. 17, 2009, which isassigned to the same assignee as the present application andincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to electronics for processinganalog signals, and more specifically but not exclusively to a tunablefilter circuit comprising acoustic resonators.

BACKGROUND INFORMATION

The considerable development of mobile telephony with its latestenhancements requires the use of increasingly sophisticated tunablefilters.

Considering in particular the Wideband Code Division Multiple Access(WCDMA) standard for the 3rd generation mobile telephony, based on 2.14Ghz, it can be considered to realize bandpass-type filter circuitsrequiring the use of resonator circuits. But making such circuits usingpassive devices of the LC-type is particularly delicate and it is evenmore difficult to integrate such circuits into a semiconductor product.

Using SAW resonators is known, unfortunately, such resonators do notallow embedding in an integrated circuit.

It has been sought to integrate a BAW-type acoustic resonator in anintegrated circuit, but manufacturing of such resonators is particularlydifficult to control. French Patent Application No. 03 15480, filed on29 Dec. 2003, describes how to realize a filter element comprising a BAWresonator.

However, combining independent filter elements in order to make asophisticated filter circuit remains a delicate operation since itcomprises combining a great number of components, in particular ofinductive resistors, varactors, and BAW resonators.

In particular, all components, and more particularly inductiveresistors, should have a high coefficient of quality. Moreover, it isimportant to make sure that inductive resistors are not mutuallydisrupting.

Generally, it would be desirable to reduce as much as possible theoccupied surface in an integrated circuit. It is indeed current that aplanar inductive resistor on a substrate of silicon occupies a surfaceabout 400×400 micrometers. It is clear that a great number of inductiveresistors is then crippling to integrated circuit manufacturing.

Indeed, it is pointed out that the typical size of a BAW resonator isabout 150×150 micrometers.

BRIEF SUMMARY OF THE INVENTION

The purpose of an embodiment of the invention is to solve theabove-described problems.

The purpose of an embodiment of the present invention is to provide atunable filter circuit optimized for embedding in a semiconductorproduct.

Another embodiment of this invention provides a tunable filter circuitcomprising varactor circuits, inductive resistors and BAW-typeresonators arranged in a particularly optimized way in order to reducecluttering in a semiconductor product while allowing high performances.

Another embodiment of this invention provides a tunable filter circuit,comprising BAW-type resonators, particularly adapted to the realizationof a mobile phone.

One embodiment of the invention provides a tunable filter circuitcomprising first and second inputs and first and second outputs.

The circuit comprises at least a primary four-pole circuit including, incascade:

-   -   a first varactor having a first electrode connected to said        first input and a second electrode;    -   a first inductive resistor having a first electrode connected to        the second electrode of the first varactor and having a second        electrode connected to the second input;    -   a secondary four-pole circuit comprising first, second, third        and fourth BAW-type resonators.    -   a second inductive resistor connected in parallel to both        outputs of the secondary four-pole circuit;    -   a second varactor having a first electrode connected to the        first output of said secondary four-pole circuit, and a second        electrode.

The secondary four-pole circuit is assembled in such a way that thefirst and second resonators have a first electrode connected to thefirst input of the secondary four-pole circuit, and a second electrodeconnected to first and second outputs of the secondary four-polecircuit, respectively. Similarly, the third and fourth resonators have afirst electrode connected to the second input of the secondary four-polecircuit and a second electrode connected to the second and first outputsof the secondary four-pole circuit, respectively.

Such a circuit that requires only two inductive resistors and allowsrealization of a particularly effective filtering unit when theinductive resistors values are chosen so as to correspond to BAWresonator parallel resonant frequencies.

Indeed, in this case, thanks to the capacitive adjustment element madeup by these varactors, a particularly effective filter, which is closeto a resonant LC unit having four inductive resistors, is obtained, withonly with two inductive resistors.

Thus, considerable surface is saved inside a semiconductor product.

Moreover, it can be noted that the circuit can be easily embedded inseveral distinct substrates, and in particular in a substrate ofIPAD-type ensuring good quality performance for passive devices and in asilicon-type substrate allowing the realization of varactors.

In one embodiment, the circuit is made up of a cascade comprising afirst capacitor in parallel, a first primary four-pole circuit, a secondcapacitor in parallel, a second primary four-pole circuit identical tothe first primary four-pole circuit and finally a third capacitor inparallel.

Thus, with only four inductive resistors, a particularly efficientfilter circuit is obtained, whose frequency can also be tuned.

In one embodiment, both primary four-pole circuits will be connected inorder to form a differential structure.

In an embodiment, inductive resistors are provided on an IPAD-typesubstrate whereas varactors are on a silicon substrate; BAW resonatorsbeing on a distinct substrate.

An embodiment of the invention also allows the realization of anacoustic resonant circuit meant to be embedded in a semiconductorproduct comprising a BAW-type resonator having first and second resonantfrequencies, characterized in that it comprises:

-   -   a first substrate, of the IPAD-type, on glass comprising an        inductive resistor for canceling said second resonant frequency    -   a second substrate comprising a capacitive adjustment element        allowing to tune said resonator to said first resonant        frequency.

In an embodiment, the capacitive adjustment element is an activecomponent (such as a diode or MOS transistor).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other features of one or more embodiments of the invention will be madeclear when reading the following description and drawings, only given byway of nonrestrictive examples. In the accompanying drawings:

FIG. 1 illustrates the schematic circuit diagram of a filter circuit inaccordance with an embodiment the present invention, having adifferential structure.

FIG. 2 illustrates an embodiment of the filter circuit, based on anIPAD-type substrate, a substrate for BAW resonators and a siliconsubstrate for varactors.

FIG. 3 illustrates an embodiment of an IPAD substrate in accordance withthe present invention, allowing interfacing with two BAW substrates andone ASIC substrate.

FIG. 4 illustrates an embodiment of the topography of the substratemeant to receive BAW components

FIGS. 5 and 6 illustrate an example transformation of the filter circuitinto an equivalent circuit comprising inductive resistors in parallel oneach BAW resonator.

FIG. 7 illustrates a second example transformation leading to anequivalent diagram in which the varactor is in series within each arm ofthe four-pole circuit.

FIG. 8 illustrates the schematic circuit diagram of the basic elementobtained with the filter circuit according to an embodiment of theinvention.

FIG. 9 a points out the principle of both resonant frequencies of a BAWresonator, series and parallel.

FIG. 9 b illustrates the equivalent diagram of an embodiment of a BAWresonator.

FIG. 10 shows a structure of a typical bandpass filter relating to anembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of an integrable tunable filter circuit comprising a set ofBAW resonators are described herein. In the following description,numerous specific details are given to provide a thorough understandingof embodiments. One skilled in the relevant art will recognize, however,that the invention can be practiced without one or more of the specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures, materials, or operations are not shownor described in detail to avoid obscuring aspects of the invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

FIG. 1 shows the architecture of a tunable filter circuit, in accordancewith one embodiment of the present invention, which has a differentialstructure. The circuit is particularly adapted to the realization of afilter circuit for a UMTS 3G mobile phone, allowing extraction of thevarious channels that compose the available emission and/or receptionband. It is only one example of realization and people qualified in theart will be able to adapt the teachings of the invention to realize anyother tunable filter circuit.

The filter circuit according to one embodiment of the present inventionis based on a parallel capacitor 19, a first primary four-pole circuit61, a parallel capacitor 29, a second primary four-pole circuit 62 and athird parallel capacitor 30, in cascade.

Each primary four-pole circuit is based on a secondary four-pole circuit(resp. 10 or 20) composed of four resonators of the BAW-type (BulkAcoustic Resonator). As it is known, BAW-type resonators are arrangedwithin a volume delimited between a bottom electrode (B) and a topelectrode (T) so that the acoustic wave develops in said volume.

As can be seen in FIG. 1, the first secondary four-pole circuit 10 hasfirst and second inputs that are connected to a first electrode (of typeT) of a first BAW resonator 11 and to a first electrode (of type T) of asecond BAW resonator 14, respectively. The secondary four-pole circuit10 also has first and second outputs that are respectively connected toa second electrode (B) of resonator 11 and to a second electrode (B) ofresonator 14.

Secondary four-pole circuit 10 further has a third BAW resonator 13having a first electrode (T) connected to the second input and a secondelectrode (B) connected to the first output.

Secondary four-pole circuit 10 finally has a fourth BAW resonator 12having a first electrode (T) connected to the first input of four-polecircuit 10 and a second electrode (B) connected to the second output offour-pole circuit 10.

The structure of secondary four-pole circuit 20 is exactly similar tothe structure of secondary four-pole circuit 10, resonators 11, 12, 13and 14 being simply replaced by resonators 21, 22, 23 and 24,respectively. Therefore, connection of these resonators will not befurther detailed.

As can be seen in FIG. 1, the filter circuit according to one embodimentof the invention comprises first and second inputs noted IN1 and IN2respectively.

First input IN1 is connected to a first electrode of first capacitor 19(C_(t)) and to a first electrode of a first varactor 17 (C_(v)).Varactor 17 has a second electrode connected to a first electrode of afirst inductive resistor 15 (L₀) and connected to the first input offour-pole circuit 10. Second input IN2 is connected to a secondelectrode of capacitor 19, to the second electrode of inductive resistor15 and to the second input of four-pole circuit 10.

The first output of four-pole circuit 10 is connected to a firstelectrode of a second inductive resistor 16 (L₀) and to a firstelectrode of a second varactor 18 (C_(v)). Varactor 18 has a secondelectrode that is connected to a first electrode of second capacitor 29(C23), to a first electrode of a third inductive resistor 26 (L₀) and tothe first input of second four-pole circuit 20.

The second output of four-pole circuit 10 is connected to the secondelectrode of inductive resistor 16, to the second electrode of capacitor29 and to a first input of a third varactor 27 (C_(v)). Varactor 27 hasa second electrode connected to the second electrode of inductiveresistor 26 and to the second input of four-pole circuit 20.

The first output of four-pole circuit 20—which is also the first outputOUT1 of the filter circuit—is connected to a first electrode of a fourthinductive resistor 25 (L₀) and to a first electrode of third fixedcapacitor 30 (C_(t))

The second output of four-pole circuit 20 is connected to the secondelectrode of inductive resistor 25 and to a first input of a fourthvaractor 28 (C_(v)). Varactor 28 has a second electrode connected to thesecond electrode of capacitor 30 and to output OUT2 of the filtercircuit.

With reference to FIG. 2, concrete realization of the filter circuit ofFIG. 1, which has a very particular aptitude to embedding in asemiconductor product, will now be explained.

It is noted that the filter circuit comprises a first module made up ofa first substrate 31 on which are arranged passive integrated circuits,in particular inductive resistors 15, 16, 25 and 26. Thus, componentsshowing particularly high quality coefficients can be realized. In oneembodiment, substrate 31 is carried out by means of a technology knownas Integrated Passive Device Technology (IPAD). As it is known, thisIPAD technology makes it possible to make passive devices provided on aglass substrate, and showing an excellent coefficient of quality.Therefore, the inductive resistors that are arranged on substrate 31exhibit a high quality factor Q.

When an embodiment of the invention is applied to the realization of afilter circuit for mobile telephony, the already existing IPAD substratecan be advantageously used to produce the BALUN. Thus, withoutadditional cost, it is possible to obtain a BALUN with very lowinsertion losses (˜1 dB).

The filter circuit then comprises a second module composed of asubstrate 32—typically a silicon substrate—on which electronic circuitsrealized using MOS-type or bipolar transistors, and varactors arearranged, thus allowing the realization of the previously describedtunable filter. Substrate 31 comprises one or more substrates (thefigure showing an example of two substrates 33 and 34) on which arearranged eight BAW resonators of the circuit of FIG. 1. A module-typeassembly is thus obtained.

Flip-chip (tin-lead) connections 35 are used for connection betweensubstrate 31 and substrates 32, 33 and 34.

The architecture illustrated in FIG. 2 can then be even flip-chipped ona dielectric substrate inside a body to realize the final semi productconduct. The constitution of such flip-chips is not part of thisinvention and will consequently not be further described.

As can be seen with topographies of substrates IPAD 31, ASIC 32 and BAW33 and 34, the filter circuit of FIG. 1 allows an arrangement with aminimum number of flip-chip connections, while making it possible toclearly separate the location of the various components on theirrespective substrates. Thus, it is ensured that combination of inductiveresistors with high quality coefficients, of effective BAW circuits andof varactors allowing adjustment of the filter circuit will be possible,which is a considerable advantage for realizing an efficient filtercircuit.

With reference to FIG. 3, one embodiment of an IPAD substrate 31 inaccordance with present invention will now be described. There are shownthe four planar inductive resistors 15, 16, 25 and 26 of FIG. 1.

Moreover, the most important contact surfaces of the flip-chips forconnection of substrates BAW 33 and 34 and for ASIC substrate 32 areillustrated.

The connections between IPAD substrate 31 and ASIC substrate 32 aremainly ensured by contact surfaces A, B, C, G, L, M, N, L′, C′ and G′.

In one embodiment, inputs IN1-IN2 and outputs OUT1-OUT2 are formed onIPAD substrate 31.

Signal IN1 (resp. IN2) arrives on contact surface A (resp. B) whichmakes it possible to offset it to ASIC substrate 32. Fixed capacitor 19is provided on ASIC substrate 32 between surfaces A and B, and varactor17 between contact surfaces A and C. The latter thus makes it possibleto bring the electric signal back on IPAD substrate 31 and to carry itto surfaces D and E that ensure transmission to electrodes T of BAWs 11and 12.

FIG. 4 more specifically illustrates the structure of four-pole circuit10 (being understood that the structure of four-pole circuit 20 will beidentical). A first horizontal bar 51, located above the structure,allows connection of surfaces E and D to T-type (Top) electrodes of BAWresonators 11 and 12. A second horizontal bar 52 makes it possible toestablish a connection between contact surfaces I and H the type-Telectrodes of BAW resonators 13 and 14.

A third bar 53, located vertically and below horizontal bars 51 and 52,is used for bottom electrodes of BAW resonators 11 and 13, and forcontact surfaces K and F. Similarly, a fourth vertical bar 54, alsoarranged below bars 51 and 52, realizes B-type electrodes of BAWresonators 12 and 14.

Referring back to the diagram of FIG. 4, the second electrode ofvaractor 17 is therefore connected, via contact surfaces C then D, tothe top electrodes of BAW resonators 11 and 12. Contact surface E, whichis arranged between the two vertical bars 53 and 54, allows a connectionnearest to the first electrode of the inductive resistor 15, whosesecond electrode can be connected to substrate BAW 33 via surface I.

Second inductive resistor 16 is connected to substrate 33 via twocontact surfaces K and J, the latter being also connected to contactsurface L.

Input IN2 is connected via surface H to the top electrodes (T) of BAWresonators 13 and 14.

Both output signals of four-pole circuit 10, brought back to the IPADsubstrate by means of contact surfaces F and J, are transmitted tocontact surfaces G and L, respectively.

Contact surface G then makes it possible to bring back the signal outputfrom the first four-pole circuit 10 to the first electrode of varactor18 on the ASIC substrate, the second electrode of varactor 18 beingconnected to surface G′ allowing signal transmission to second four-polecircuit 20.

Contact surface L makes it possible to transmit the voltage of thesecond left four-pole circuit 10 to the first electrode of varactor 27on the ASIC substrate, the second electrode of varactor 27 beingconnected to surface L′ in order to allow transmission of the signal tothe second four-pole circuit.

The voltage of the first output of four-pole circuit 20 is transmittedvia T electrodes of BAW resonators 21 and 23 to contact surface M, ascan be seen in FIG. 4. The voltage appearing on the second output offour-pole circuit 20 is transmitted via contact surface C′ to ASICsubstrate 32 and is thereby connected to the first electrode of varactor28, whose second electrode is connected to surface N that makes itpossible to bring the output signal back on the IPAD substrate.

In an embodiment, ASIC substrate 32 also comprises capacitors 29 and 30,respectively connected between surfaces LG′ and N-M.

As can be seen, the connection between IPAD substrate 31 and BAWsubstrate 33 is carried out by surfaces E, D, F, I, H, K and J while theconnection between IPAD substrate 31 and ASIC substrate 32 is done viasurfaces A, B, C, G, L, N and M.

Connections between IPAD substrate 31 and substrate BAW 34 are perfectlysymmetrical to those existing for substrate 33. Only surfaces L′, C′ andG′ are illustrated as they correspond to surfaces L, C and G that wereshown for substrate BAW 32.

The filter circuit of an embodiment of the invention makes it possibleto harmoniously distribute the various components between the IPADsubstrate, BAW substrate(s) and the ASIC substrate, while requiring onlya reduced number of flip-chip or connections.

This is a significant advantage of an embodiment of the invention.

It will now be shown that, with only four inductive resistors, thefilter circuit carries out a sophisticated filtering function identicalto a filter comprising eight inductive resistors.

Indeed, considering the filter circuit of an embodiment of theinvention, and referring again to FIG. 5, it can be observed that thecircuit is made up by the following elements in cascade:

-   -   fixed capacitor C_(T)    -   a first primary four-pole filter circuit 61 comprising secondary        four-pole circuit 10,    -   capacitor C₂₃    -   a second primary four-pole filter circuit 62 comprising        secondary four-pole circuit 20,

associated to passive elements C_(v) and L₀

Each primary four-pole circuit 61 or 62 can be represented in anequivalent form, such as illustrated in FIG. 6, where it can be seenthat the inductive resistor of value L₀ identical to that of inductiveresistors 15, 16, 25 and 26, is directly mounted in parallel with eachBAW resonator.

It can also be shown, by means of a transformation illustrated in FIG.7, that each four-pole circuit 61 and 62 can then be designed with a newequivalent electric diagram where each branch of the four-pole circuitcan be replaced by an element, shown in FIG. 8, comprising a varactor 91and a BAW resonator 92 in series, the BAW resonator comprising aninductive resistor 93 in parallel.

In the filter circuit according to an embodiment of the invention,inductive resistor 93 (of value L₀) is tuned so as to be resonating withthe parallel capacity of the BAW resonator with which it is associated.

An extremely significant result is then obtained. Indeed, the acousticresonators have two very close resonant frequencies, respectively fs(series) and FP (parallel), as is illustrated in FIG. 9 a. Referring tothe equivalent electric diagram illustrated in FIG. 9 b, it amounts toconsidering two resonant circuits of the LC-type, respectively seriesand parallel.

Typically, both resonant circuits are simultaneously used for filtering,as it is the case in document “RF MEMS Circuit Design for WirelessCommunications”, Hector J. De Los Santos, Artech House, ISBN 1-58033329-9, 2002, p. 163 and following.

In an embodiment of the invention, the parallel frequency is canceled bymeans of an equivalent inductance (L0) selected in the vicinity of theparallel frequency. Then, the series frequency can be very simply actedupon to make the filter tunable.

This makes it possible to produce a complex filter, as illustrated inFIG. 10, by means of a circuit that is easy to manufacture.

It will be noted that a varactor is used to realize a capacitiveadjustment element in one embodiment. This component being well known bypeople qualified in the art, its realization will not be furtherdetailed therein. It could also be substituted by other capacitiveadjustment element.

It will also be noted that fixed capacitors 19, 29 and 30 could bearranged on the IPAD instead of ASIC substrate 32.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe invention to the precise forms disclosed. While specific embodimentsand examples are described herein for illustrative purposes, variousequivalent modifications are possible within the scope of the inventionand can be made without deviating from the spirit and scope of theinvention.

These and other modifications can be made to the invention in light ofthe above detailed description. The terms used in the following claimsshould not be construed to limit the invention to the specificembodiments disclosed in the specification and the claims. Rather, thescope of the invention is to be determined entirely by the followingclaims, which are to be construed in accordance with establisheddoctrines of claim interpretation.

1. An acoustic resonant circuit integrated in a semiconductor productincluding a bulk acoustic wave (BAW)-type resonator having first andsecond resonant frequencies, the acoustic resonant circuit comprising: afirst substrate, of an integrated passive device and active devices(IPAD)-type, made of glass, including an inductive resistor having firstand second input terminals to cancel the second resonant frequency; asecond substrate including a first capacitive adjustment element toenable tuning of said resonator to said first resonant frequency; and afour-pole circuit having first and second input terminals respectivelycoupled to the first and second terminals of the inductive resistor andhaving first and second output terminals, the four-pole circuitincluding a first plurality of resonators that includes the BAW-typeresonator; an inductive element having first and second terminalsrespectively coupled to the first and second output terminals of thefour-pole circuit; and a second capacitive adjustment element having afirst terminal coupled to the first terminal of the inductive elementand having a second terminal, wherein the first plurality of resonatorshave the second resonant frequency.
 2. The circuit according to claim 1wherein said first capacitive adjustment element is a varactor.
 3. Thecircuit according to claim 1 wherein said second substrate is a siliconsubstrate.
 4. The circuit according to claim 1, further comprising athird substrate that includes said BAW-type resonator.
 5. The circuitaccording to claim 4, further comprising connections between said first,second, and third substrates.
 6. The circuit according to claim 1,further comprising: first and second filter input terminals; wherein thefirst capacitive adjustment element having a first terminal coupled tothe first filter input terminal and having a second terminal; andwherein said inductive resistor has a first terminal coupled to thesecond terminal of the first capacitive adjustment element and furtherhas a second terminal coupled to the second filter input terminal.
 7. Anacoustic resonant circuit integrated in a semiconductor product, theresonant circuit comprising: a resonator having first and secondresonant frequencies; a first substrate made of glass and including afirst inductive element to cancel said second resonant frequency; asecond substrate including a capacitive adjustment element to enable totune said resonator to said first resonant frequency; electricalconnections between said resonator, said first inductive element, andsaid capacitive adjustment element; and a first four-pole circuit havingfirst and second input terminals respectively coupled to the first andsecond terminals of the first inductive element and having first andsecond output terminals, the first four-pole circuit including a firstplurality of resonators that includes said resonator.
 8. The circuit ofclaim 7 wherein said resonator is a bulk acoustic wave (BAW)-typeresonator.
 9. The circuit of claim 7 wherein said capacitive adjustmentelement is a varactor.
 10. The circuit of claim 7 wherein said secondsubstrate is a silicon substrate.
 11. The circuit of claim 7, furthercomprising a third substrate that includes said resonator.
 12. Thecircuit of claim 11 wherein said first, second, and third substrates arepart of a flip-chip arrangement.
 13. The circuit of claim 7, furthercomprising: first and second filter input terminals; wherein saidcapacitive adjustment element is a first capacitive adjustment elementhaving a first terminal coupled to the first filter input terminal andhaving a second terminal; wherein said first inductive element has afirst terminal coupled to the second terminal of the first capacitiveadjustment element and further has a second terminal coupled to thesecond filter input terminal; a second inductive element having firstand second terminals respectively coupled to the first and second outputterminals of the first four-pole circuit; and a second capacitiveadjustment element having a first terminal coupled to the first terminalof the second inductive element and having a second terminal, whereinthe first plurality of resonators have said second resonant frequency.14. An acoustic resonant circuit integrated in a semiconductor productincluding a bulk acoustic wave (BAW)-type resonator having first andsecond resonant frequencies, the acoustic resonant circuit comprising: afirst substrate, of an integrated passive device and active devices(IPAD)-type, made of glass, including an inductive resistor to cancelthe second resonant frequency; a second substrate including a capacitiveadjustment element to enable to tune the resonator to the first resonantfrequency; first and second filter input terminals, wherein thecapacitive adjustment element is a first capacitive adjustment elementhaving a first terminal coupled to the first filter input terminal andhaving a second terminal, wherein the inductive resistor is a firstinductive element having a first terminal coupled to the second terminalof the first capacitive adjustment element and having a second terminalcoupled to the second filter input terminal; a first four-pole circuithaving first and second input terminals respectively coupled to thefirst and second terminals of the first inductive element and havingfirst and second output terminals, the first four-pole circuit includinga first plurality of resonators that includes the BAW-type resonator; asecond inductive element having first and second terminals respectivelycoupled to the first and second output terminals of the first four-polecircuit; and a second capacitive adjustment element having a firstterminal coupled to the first terminal of the second inductive elementand having a second terminal, wherein the first plurality of resonatorshave the second resonant frequency, and wherein the first and secondinductive elements have an inductance in a vicinity of the secondresonant frequency.
 15. The circuit according to claim 14, furthercomprising a third substrate that includes the BAW-type resonator. 16.The circuit according to claim 15, further comprising connectionsbetween the first, second, and third substrates.
 17. An acousticresonant circuit integrated in a semiconductor product, the resonantcircuit comprising: a resonator having first and second resonantfrequencies; a first substrate made of glass and including an inductiveresistor to cancel the second resonant frequency; a second substrateincluding a capacitive adjustment element to enable to tune theresonator to the first resonant frequency; electrical connectionsbetween the resonator, the inductive resistor, and the capacitiveadjustment element; first and second filter input terminals, wherein thecapacitive adjustment element is a first capacitive adjustment elementhaving a first terminal coupled to the first filter input terminal andhaving a second terminal, wherein the inductive resistor is a firstinductive element having a first terminal coupled to the second terminalof the first capacitive adjustment element and having a second terminalcoupled to the second filter input terminal; a first four-pole circuithaving first and second input terminals respectively coupled to thefirst and second terminals of the first inductive element and havingfirst and second output terminals, the first four-pole circuit includinga first plurality of resonators that includes the resonator; a secondinductive element having first and second terminals respectively coupledto the first and second output terminals of the first four-pole circuit;and a second capacitive adjustment element having a first terminalcoupled to the first terminal of the second inductive element and havinga second terminal, wherein the first plurality of resonators have thesecond resonant frequency, and wherein the first and second inductiveelements have an inductance in a vicinity of the second resonantfrequency.
 18. The circuit of claim 17 wherein the resonator is a bulkacoustic wave (BAW)-type resonator.
 19. The circuit of claim 17, furthercomprising a third substrate that includes the resonator.
 20. Thecircuit of claim 19 wherein the first, second, and third substrates arepart of a flip-chip arrangement.